Prevalence of bovine trypanosomiasis in Côte d’Ivoire: Systematic review and meta-analysis

Bovine trypanosomiasis is a parasitic disease caused by protozoans of the genus Trypanosoma. The disease cause economic losses in livestock production. In order to determine the status of research on this disease in Côte d’Ivoire, we used the systematic review method and meta-analysis. Three electronics databases, namely Google Scholar, PubMed and CrossRef were used to search for publications on trypanosomiasis prevalence that met our inclusion criteria. Twenty five articles were identified, 11 of which met the inclusion criteria. Bovine trypanosomiasis prevalence of 2.99% (95% confidence interval [CI]: 2.96% – 3.01%) to 25.28% (95% CI: 25.17% – 25.38%) were recorded between 1960 and 2021. The analyses showed that the most infected regions were the Bagoue 11.26% (95% CI: 11.25% – 11.27%), Bounkani 14.94% (95% CI: 14.93% – 14.95%), Gbeke 10.34% (95% CI: 10.33% – 10.35%), Marahoue 13.79% (95% CI: 13.78% – 13.80%), Poro 8.50% (95% CI: 8.49% – 8.51%), and Tchologo 11.83% (95% CI: 11.82% – 11.84%).The most sensitive diagnostic method used was the polymerase chain reaction (PCR). The species of trypanosomes diagnosed were Typanosoma vivax 4.99% (95% CI: 4.97% – 5.01%), T. congolense 1.51% (95% CI: 1.49% – 1.52%), and T. brucei 0.61% (95% CI: 0.59% – 0.62%). Despite some variation, the prevalence of bovine trypanosomiasis in Côte d’Ivoire caused mainly by T. vivax has increased in the years between 1977 and 2017. Efforts to control tsetse and other mechanical vectors should also be put in place to minimize its transmission. Contribution The authors studied the prevalence of bovine trypanosomiasis using the systematic review method and MA in order to determine the status of research on this disease in Côte d’Ivoire.


Introduction
Trypanosomes are flagellate unicellular protozoa belonging to the family Trypanosomatidae and the genus Trypanosoma (Aubry 2012). Many of the species that cause both animal and human trypanosomiasis belong to the genus Trypanosoma (Mekata et al. 2013). African animal and human trypanosomiasis are transmitted by tsetse flies of the genus Glossina. Nevertheless, some species have evolved to adapt to mechanical transmission, which has let them to spread beyond Africa's tsetse zone, resulting in the 'Nagana' cattle wasting disease. Trypanosomes can be mechanically transmitted by hematophagous flies of the genera Stomoxys and Tabanus (Bafort, Kageruka & Timperman 1973). The ability of the parasites to remain in the vector's mouth cavity is necessary for mechanical transmission. Therefore, the success of parasite transmission increases with the length of the blood-sucking gap of the vector between an infected and an uninfected animal (Desquesnes et al. 2013). The pathogens responsible for the most important trypanosomal infections in livestock are Trypanosoma congolense (Mackenzie et al. 1978) (savannah group), Trypanosoma vivax (Ziemann 1905) and Trypanosoma brucei (Difonzo & Bordia 1998). In Africa, trypanosomes are mainly found in the humid or subhumid areas (Sané et al. 2000) estimated to cover about 10 million km 2 . Trypanosomal infections in this zone constitute a major constraint to livestock development. Indeed, there are nearly 50 million cattle and about 70 million small ruminants continuously exposed to trypanosomiasis risk (Paylhard 2019;Fandamu et al. 2005). Typanosomiasis has a significant socio-economic impact and limits animal productivity in Africa with direct and indirect losses estimated at $4.5 billion (De La Rocque 2001, 2003. Côte d'Ivoire is one of the most affected countries (Douati, Kupper & Kotia 1986). This is due to its vegetation, climate and hydrographic network which constitute an ecosystem favourable to Bovine trypanosomiasis is a parasitic disease caused by protozoans of the genus Trypanosoma. The disease cause economic losses in livestock production. In order to determine the status of research on this disease in Côte d'Ivoire, we used the systematic review method and meta-analysis. Three electronics databases, namely Google Scholar, PubMed and CrossRef were used to search for publications on trypanosomiasis prevalence that met our inclusion criteria. Twenty five articles were identified, 11 of which met the inclusion criteria. Bovine trypanosomiasis prevalence of 2.99% (95% confidence interval [CI]: 2.96% -3.01%) to 25.28% (95% CI: 25.17% -25.38%) were recorded between 1960 and 2021. The analyses showed that the most infected regions were the Bagoue 11.26% (95% CI: 11.25% -11.27%), Bounkani 14.94% (95% CI: 14.93% -14.95%), Gbeke 10.34% (95% CI: 10.33% -10.35%), Marahoue 13.79% (95% CI: 13.78% -13.80%), Poro 8.50% (95% CI: 8.49% -8.51%), and Tchologo 11.83% (95% CI: 11.82% -11.84%).The most sensitive diagnostic method used was the polymerase chain reaction (PCR). The species of trypanosomes diagnosed were Typanosoma vivax 4.99% (95% CI: 4.97% -5.01%), T. congolense 1.51% (95% CI: 1.49% -1.52%), and T. brucei 0.61% (95% CI: 0.59% -0.62%). Despite some variation, the prevalence of bovine trypanosomiasis in Côte d'Ivoire caused mainly by T. vivax has increased in the years between 1977 and 2017. Efforts to control tsetse and other mechanical vectors should also be put in place to minimize its transmission. In order to give a general overview of the epidemiology of bovine trypanosomiasis in Côte d'Ivoire, this systematic review and meta-analysis (MA) were conducted. Specifically, to analyse the trypanosomes species distribution; evaluate methods of detection and determine the prevalence of the disease.

Search strategy and inclusion criteria
Following the guidelines in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guide, the systematic review (SR) and MA were carried out (Moher et al. 2009 (Harzing 2007). Articles from PubMed were imported directly into Rayyan QCRI. References that were identical in terms of location, numerator, denominator and study period were eliminated. After a preliminary title and abstract screening, the complete texts of articles that were considered to be potentially relevant were examined. The bibliographies of the articles that were included were examined to locate additional pertinent and qualified articles.

Inclusion and exclusion criteria
Relevant literature was searched, evaluated and analysed according to the PRISMA statement (Harzing 2007;Kamioka 2019). Inclusion and exclusion criteria, as well as search syntaxes, were predefined. Initially, references were selected based on their titles. Emphasis was placed on articles describing the epidemiology of bovine trypanosomiasis in Côte d'Ivoire, without limiting the date of publication. A previously stated inclusion criteria were established to include articles that offered relevant quantitative information on the epidemiology of bovine trypanosomiasis.
The references retained after the initial selection were analysed according to the abstract. Abstracts without full text, review articles, redundant information and studies that only describe the diagnosis of bovine trypanosomiasis were excluded. The full-text file of the publication was included if the data in the abstract were insufficient for evaluation. The following inclusion criteria were used to examine full-text publications: (1) A publication should contain information on cattle in Côte d'Ivoire; (2) contain information on the prevalence incidence and distribution of trypanosome species in cattle in Côte d'Ivoire.
The following causes contributed to the exclusion of full-text publications: (1) unspecified diagnostic test; (2) sample source not specified; (3) review articles; (4) articles reporting data published elsewhere; (5) cases reports based only on clinical signs; (6) epidemic reports without a lab confirmation and (7) reports of prevalence in any diagnostic test experimentation.
Publications with pertinent epidemiological data were included in the quantitative MA to determine the overall prevalence. Information such as cattle breeds, trypanosomes species responsible for the infections, sample size, method of diagnosis and prevalence were included in the analysis.
Prevalence estimation was performed after diagnostic tests categorisation. Thus, three categories were used to group the diagnostic tests: (1) parasitological methods such as wet blood smears, stained blood smears and microhematocrit concentration; (2) serological tests using antibody-based enzyme-linked immunosorbent assay (Ab-ELISA) and antigen-based enzyme-linked immunosorbent assay (Ag-ELISA) and (3) molecular tests including ordinary polymerase chain reaction (PCR) with various primers.

Data extraction
Reference information such as author's name, title and publication year were recorded in the database. The following data were extracted from the included publications: study area (department, region), periods of sample collection, cattle breeds, sample size, origin of the sample collected, diagnostic method used, number of positives, prevalence. Prevalence of trypanosomiasis was defined as the frequency of infection with T. congolense, T. vivax and T. brucei in a given population at a given time.
For articles that only reported the total number of animals sampled and the prevalence, the number of positives was estimated. Similarly, prevalence was estimated for article that reported only the number of samples and the number of positives. Case reports containing the required information, with the exception of prevalence data, were also included in the analysis. All data were recorded in an MS Excel spreadsheet.

Statistical analysis
The data analysis was performed in several steps. Firstly, the mean prevalence was estimated by summing the number of cases in all studies included, divided by the total number of cattle sampled. If the year of data collection was not specified in the research, the publication year minus one (n−1) was considered. Secondly, the estimation of the total prevalence of bovine trypanosomiasis in the general sample size and their 95% confidence intervals (CIs) were evaluated by a random-effects. In these studies, heterogeneity was assessed by Cochran's Q-test and the inverse of variance index (I). The variance index (I-squared) reflects the percentage of overall variation between studies due to heterogeneity and not by chance. I-squared values of 25%, 50% and 75%, respectively, indicate low, moderate and high degrees of heterogeneity. I-squared values of 0% imply that no heterogeneity was detected. On a standardised scale, Q is the weight of squares. It is presented as a p-value, with low values suggesting heterogeneity.
Subgroup analyses were carried out to identify potential sources of study heterogeneity. The study area (region and department), sample size, cattle breed, blood source, diagnostic method and trypanosome species were variables considered in the subgroup analysis. A funnel plot and an Egger plot allowed us to examine by visualisation the bias between studies. In addition, the statistical significance of bias was tested with Egger's regression skewness test (Egger et al. 1997

Ethical considerations
This article followed all ethical standards for research without direct contact with human or animal subjects.

Literature selection
A total of 1902 potential articles ( Figure 1) were obtained from the literature searches. After reviewing titles, abstracts and excluding repeated articles from the database, for full text review, 176 articles were chosen. After examination of these articles based on our selection criteria, we obtained 25 articles that were eligible for systematic review. Of these 25 articles, 11 were selected to make the MA.

Geographical distribution of bovine trypanosomiasis
The studies included in this review were conducted between 1979 and 2016 in 26 departments grouped into 12 regions The spatial distribution of prevalence is illustrated in Figure 2, which shows that studies on the geographical distribution of bovine trypanosomiasis were mainly conducted in the northern, northwestern, northeastern and central regions of
The meta-regression (Figure 3 and Figure 4) by survey year (considered as continuous variable) indicated a significant increase of the prevalence of bovine trypanosomiasis (Z = -11.13; Q = 191.05; degree of freedon [df] = 10; p < 0.001). Figure 3 and Figure 4 show the scatter plot of the regression of mean prevalence with survey year. The p-value for the survey year was < 0.05, indicating a stable pattern over time and space.

Discussion
This study presents a systematic review of bovine trypanosomiasis prevalence and its pathogens in Côte d'Ivoire. The analyses indicate that bovine trypanosomiasis prevalence in Côte d'Ivoire has significantly increased over the years.
The increase in prevalence could be explained by several factors including limited number of studies and political prioritisation of the eradication of human African Trypanosomiasis over bovine trypanosomiasis. Since the first outbreak of the African trypanosomiasis, 11 studies over a period of 50 years have been conducted on bovine trypanosomiasis and the majority of these studies were concentrated in the last 18 years. Control and eradication of animal Trypanosomiasis have also been hampered by the various military-political crises in Côte d'Ivoire since 2000s. Tsetse fly control efforts have not been successful in these areas, unlike in areas endemic to human trypanosomiasis that were under state control during these crises (Kambiré et al. 2012).
The highest prevalence was found in the northern part of Côte d'Ivoire. These results are consistent with the findings  . This zone is partly the major livestock area because of its vegetation and climate that favour livestock activity and in this area the animals have a role in the socio-cultural development and also a value ). This territory is crossed by the four major rivers, which are the Bandama, Cavally, Sassandra and Comoé. These rivers are bordered by gallery forests (Acapovi-Yao et al. 2016;Camus 1981), which are known to be preferred sites for tsetse fly development (Bokar 1997;Sokouri et al. 2014). This area has several small dense forests, where cultural rites are conducted. These small forests are off-limits and constitute a favourable biotope for the proliferation of tsetse flies. The incriminated vectors are Glossina palpalis palpalis (Robineau-Desvoidy 1830), G. palpalis gambiensis (Vanderplanck 1949) and G. tachninoides (Westwood 1830) (Acapovi- Yao et al. 2010;Gouteux & Millet 1984). According to some authors (Djohan et al. 2015;Jamonneau et al. 2003), G. palpalis gambiensis and G. tachninoides are the vectors responsible for the transmission of animal trypanosomiasis. The high prevalence in the northern zone could be because of incorrect use of trypanocides, which promotes the development of trypanosome resistance (Simo et al. 2020). Trypanosoma congolense, T. vivax and T. brucei are commonly found in the 12 regions of Sudanese zone of Côte d'Ivoire (Solano et al. 1997) and are considered to be the most important pathogens in Trypanosoma infections in these regions (Acapovi-Yao et al. 2016;Poivey et al. 1983;Yao et al. 2020). Their presence may be related to the aforementioned specific tsetse species that are found in cattle in these farming areas mainly concentrated in the northern part of Côte d'Ivoire, which is the savannah zone.
The majority of studies included in this review have used parasitological methods. These methods are dependent on a high parasitemia in infected animals and on a morphological observation, which require expertise and experience of a technician making the observations (Hailu 2019). Irrespective of the technique used, PCR proved to be the most sensitive. The technique was validated using blood samples from experimentally infected animals, revealing its higher sensitivity and specificity when compared with parasitological techniques (Cox et al. 2005;Solano et al. 1999). This confirms the place of molecular techniques as the best means of diagnosis and identification of microorganisms.
The most predominant species of Trypanosoma was T. vivax. Similar observations have also been reported in Burkina Faso (Desquesnes & Dia 2003). This might be as a result of the transmission of T. vivax by other mechanical vectors as cattle are subjected to biting flies (Tabanids and Stomoxys) while grazing. According to Desquesnes et al. (2022), T. vivax geographical distribution is the whole of sub-Saharan Africa, the South and Central American and Iran. T. congolense savannah group is the agent responsible for the most severe form of animal Trypanosomiasis (Bengaly et al. 2002).
The analyses showed that the taurine breeds (indigenous) are less parasitized than Méré (cross-breed) and Zebu breeds. Other authors (Yao et al. 2020) reported similar results; this is because of an inherited trypanotolerance trait in taurines. Indeed, thanks to this genetic predisposition, these animals remain productive in these endemic areas.
With the Méré, a breed resulting from cross-breeding taurines and zebu, the objective was to create a more hardy breed with this trypanotolerant trait. Unfortunately, high prevalence of trypanosomiasis among the Mérés suggests otherwise (Sokouri et al. 2009).

Conclusion
This work represents the first attempt of a systematic review of bovine trypanosomiasis in Côte d'Ivoire. This review of systematic and MA provides comprehensive information on geographic distribution, infected cattle breeds and prevalence of bovine trypanosomiasis. The findings indicate variation in estimated prevalence depending on the diagnostic test used. Estimated bovine trypanosomiasis prevalence is high; however, variability was observed between departments and survey years. Based on the economic importance of the disease in livestock production, its detection in cattle is of great concern. It is recommended that PCR, which was the most sensitive technique, should be used in diagnosis and to facilitate control. Risk of transmission of trypanosomiasis in cattle in Côte d'Ivoire remain high. Considering the high prevalence of trypanosomiasis in crossbred cattle, crossbreeding in farms should be controlled. As T. vivax was one of the most important trypanosome species detected. In addition to regular tsetse control campaigns in the country, efforts to control other mechanical vectors should also be put in place.